use code like this...

Declare
  total_records number:=0;
Begin
  go_block('YOUR_MULTI_RECORD_BLOCK');
  Last_Record;
  total_records := to_number(:system.cursor_record);
  First_Record;
  For i in 1..total_records;
  Loop
      here goes your validation code...
      If condition not true Then
         Next_Record;
      End If;
  End Loop;
End;

If you want to track from which record validation begin, simple add a variable after total_records as:

  curr_record number:=to_number(:system.cursor_record);

i also faced problems with Navigational Triggers for this kind of validation. If somebody else has better idea, please inform.

we have to remember one thing that there is no limit of knowledge and ideas.